Enphase M250 Specs for off-grid, tips and tricks and results

[solarddy]

Hello all,

Time for the hidden tips and tricks to make your Enphase array go offgrid like magic.

M250's "Turn-On-244vac output" phase lock requires: Pure sine wave @ 59.99-61Hz (+/- 2hz from 60), a THD less than 2%, 244-245vac, M250's provide a "split-Phase" 245vac with provided neutral and when stacked are the most affordable reliable modular micro-inverters in the world. For a 8KW backup UPS system in a box with 30 minutes of run-time with those above specs think $15-20K. You can build one longer lasting for far cheaper.

M250's actually power up at 22Vdc, and then off again at 18Vdc automatically. So if you were to use a 24VDC battery bank you could use that to run your M250's at night if you wire them accordingly and when the voltage gets too low they would just turn off, protecting your investment. Many PWM charge controllers operate at 24VDC and have an internal timer or PE sensor which will switch the micro-inverter load to battery on a schedule.

For the base "utility" signal, any "split phase" 244vac inverter which can match the above specs will do. You will find that specs that tight are not industry standard, but they are the more expensive type inverters to maintain the less than 2% THD. Expect to spend $2000+ for a split-phase 244vac inverter like a Magnasine, SunnyBoy, Nfinity to name a few. Chinese manufacturers will turn up the voltage for you if you ask nicely but they sell very few true sine wave inverters with true "split-phase" 244vac.

After phase lock if the solar power produced is not used, the excess panels need to be turned off or diverted to battery chargers if not hooked to the grid. Every minute or so a large voltage pulse builds up and can be seen in lighting which gets that much brighter when the pulses surge. It also takes 5 minutes for the M250 micro-inverters to turn back on after they fault or experience a power loss on the utility side.

As for a battery back-up, quit goofing around and put in some batteries! Go off-grid! I suggest a 24VDC bank as it is easier to match to the M250 inverters. The specs on batteries varies greatly, the most expensive batteries may not be the best option. Get some heavy, deep cycle, well reviewed batteries and stack em up.

I will suggest a dual-use option that you may not have considered. If you use 2, Y adapters from the Solar panel output, and split the power between an inexpensive PWM controller and a M250, the PWM controller will stop charging when the battery is full automatically and the full load of the panel will go to the M250. Automation made easy.
I see no issue connecting these isolated devices in this manner and welcome any arguments against except for the MPPT one.
If you can afford MPPT, then get MPPT, if not use PWM @ 3x the rating you will be using it at for longevity of the charge controller.

My current formula is: 1 24VDC battery source, 1 M250 micro-inverter, one 30A PWM or MPPT controller for each 300+ watt solar panel for AC/DC parallel wiring configurations and maximum uptime, think more than 5 decades. The battery choice is where they get you- BANG! pay up every 3-5 years or buy super expensive batteries that last 8-10. I choose the middle route of batteries, ones that cost me 1/3 of the cost of the big boys, and only last 33% of the max life of them too with little maintenance to do except check water levels. So what if I have to change out batteries that I can recycle $$ to maintain my system every 3-5 years? Probably will need some re-tensioning and terminal cleaning anyhow.

The average internet connected family will need 300-350Ah of battery storage to go through the night with the fans, the AC, and the computers.. etc... on.

The coolest part about the M250's is that they Phase lock individually, and those phase locks are very close to true, but they are not. When performing test readings/observations on my A.C. unit, I found it was much quieter when running on phase-locked solar, the motor didn't go mmm mmm mmmm mmm like it was grunting, it went almost silent. The fan's movement of air made more noise than the compressor, and it never blows colder air then when on the solar under a bright sun. It is possible to run an Air Conditioning unit on just solar power, but you will need some things like a battery bank and/or a M250 Phase lock array.

Being an avid field theory Major, I surmised the following: The phase lock being close but not exact is generating slightly off-axis magnetic fields in the motor wiring, which act like additional little arms pushing the motor more efficiently! Or something close to that definition. I found that my computer works better too, it was "smoother" which translates to better power usage since I didn't upgrade anything except the power source.

[solarddy]

M250 AC Dongle diagram

m250 pinout diagram.jpg

This is a M250 AC dongle diagram.

[Naptown]

So how are you getting around the lack of grid? And the required grid verification?
Using another inverter to simulate the grid?
I have seen AC coupled systems using them but have not installed any.
Reason is for back up people will tend to try to live normally and deplete the batteries. The secondary inverter will not start from low voltage and entire system is dead until the batteries are charged back up.
Much prefer a standard hybrid system with cc batteries and inverter such as the schneider context.
At least the batteries will charge back up next sunny day.

[solarddy]

Off-grid is challenge for those without power bills... not!

So how are you getting around the lack of grid? And the required grid verification?
Using another inverter to simulate the grid?
I have seen AC coupled systems using them but have not installed any.
Reason is for back up people will tend to try to live normally and deplete the batteries. The secondary inverter will not start from low voltage and entire system is dead until the batteries are charged back up.
Much prefer a standard hybrid system with cc batteries and inverter such as the schneider context.
At least the batteries will charge back up next sunny day.

The point of off-grid is to provide a source of power when there is none. Going off-grid means you buy enough batteries to last the night or two, not apocalyptic scenarios where you buy to last months.

The listed specs will allow the micro-inverters to go off-grid. That is the point of this post, understanding M250's and what makes them function for off-grid use.
Yes you must induce a simulated grid, it can be with a grid-interactive inverter like the Magnasine MS4024PAE, or it can be a stand alone, like the Nfinity, but either way you have to induce a proper pure sine wave at the listed specifications for the micro-inverters to be used off-grid.

I am not just speaking of back-up systems, I am talking about off-grid designs that employ the M250 as a primary Micro-inverter whereas they provide all AC power beyond the base inverter which generates the mini-grid, fed from batteries at night and the sun during the day.

I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency power loss at solar arrays employing micro-inverters. It would be on a switch, maybe even automatic that wouldn't allow it to turn on unless AC voltage was not present during it's start-up routine checks, likely it would have to be wired to the grid and use separate grid sensing terminals on an AC input side to accomplish this. The DC input would be 24-48Vdc and the output would be a pure sine wave (2x, 122.5vac 180degree out of phase 245vac) @<2% THD +/- 2Hz from 60, a neutral and a ground. by my calculations the output would have to be only great enough to handle the feedback, so larger grids would require larger base inverters for the unused surge ripple handing. There would be a scale like 2.5K array needs 500Wt base inverter and the larger micro-grids would need larger base inverters. It could be even cooler if you could remove the additional ripple surge as heat to a dump load like a water heater. If it was very smart, like a UPS circuit, there would be non interruption in power it would just take over upon power loss. The unit may have to also be parallel-able for large grid or Macro-grids.

That "Island" inverter will be built by some company eventually for much less than the current $1600-2200. I think a product such as this would speak volumes to a homeowner who has micro-inverters for emergency back-up concerns.

Why? Because micro-inverters offer a scalable product which is easy to work with and provides basically unlimited scalability in a modular package.

[inetdog]

The point of off-grid is to provide a source of power when there is none. Going off-grid means you buy enough batteries to last the night or two, not apocalyptic scenarios where you buy to last months.

The listed specs will allow the micro-inverters to go off-grid. That is the point of this post, understanding M250's and what makes them function for off-grid use.
Yes you must induce a simulated grid, it can be with a grid-interactive inverter like the Magnasine MS4024PAE, or it can be a stand alone, like the Nfinity, but either way you have to induce a proper pure sine wave at the listed specifications for the micro-inverters to be used off-grid.

I am not just speaking of back-up systems, I am talking about off-grid designs that employ the M250 as a primary Micro-inverter whereas they provide all AC power beyond the base inverter which generates the mini-grid, fed from batteries at night and the sun during the day.

I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency on solar arrays employing micro-inverters. It would be on a switch, maybe even automatic that wouldn't allow it to turn on unless AC voltage was not present during it's start-up routine checks, likely it would have to be wired to the grid and use separate grid sensing terminals on the input side to accomplish this. The input would be 24-48Vdc and the output would be a pure sine wave (2x, 122.5vac 180degree out of phase 245vac) @<2% THD +/- 2Hz from 60, a neutral and a ground. by my calculations the output would have to be only great enough to handle the feedback, so larger grids would require larger base inverters for the unused surge ripple handing. There would be a scale like 2.5K array needs 500Wt base inverter and the larger micro-grids would need larger base inverters. It could be even cooler if you could remove the additional ripple surge as heat to a dump load like a water heater. If it was very smart, like a UPS circuit, there would be non interruption in power it would just take over upon power loss. The unit may have to also be parallel-able for large grid designs Macro-grid.

That "Island" inverter will be built by some company eventually for much less than the current $1600-2200. I think a product such as this would speak volumes to a homeowner who has micro-inverters for emergency back-up concerns.

Why? Because micro-inverters offer a scalable product which is easy to work with and provides basically unlimited scalability in a modular package.

You mean something like the SMA Sunny Island off grid inverter that is designed to work with their Sunny Boy grid tie inverters?
The key feature that this pairing includes that your idea does not is that the SI can signal the SBs to reduce their output to keep from backfeeding the SI beyond what it can use to charge the batteries. I do not know of any microinverters that will respond to such throttling signals.
The configuration that you describe seems to me to require manual monitoring to turn off individual micros to keep the generated power slightly less than the local load.
I would not trust such a system, since any lapse could blow up the off grid inverter.
Also, you absolutely MUST have a transfer switch to keep the combination of off-grid and GTI inverters from connecting to the grid while they are running in island mode.
Designing such a system safely is not trivial and is not what I would call DIY friendly either.
Anything done without the participation of a knowledgeable licensed electrician would never pass a permit inspection, or if it did would not necessarily be safe anyway.
You would be using the components in a way that was NOT within the manufacturer's design and testing process.
The micro manufacturer may provide instructions on how to configure this kind of use, but that does not by itself make it code approved or even safe.

PS: The problem in general is not the "ripple surge" that you talk about, it is simply excess power production! (With maybe some problems with low power factor loads since the GTI will by default deliver at a unit power factor only. )
Your careless, imprecise, or uneducated use of the relevant terminology make me take everything you say with a large block of salt, and I caution other forum members from jumping into this in the real world without a much better understanding of what is involved.

[solarddy]

You mean something like the SMA Sunny Island off grid inverter that is designed to work with their Sunny Boy grid tie inverters?
The key feature that this pairing includes that your idea does not is that the SI can signal the SBs to reduce their output to keep from backfeeding the SI beyond what it can use to charge the batteries. I do not know of any microinverters that will respond to such throttling signals.
The configuration that you describe seems to me to require manual monitoring to turn off individual micros to keep the generated power slightly less than the local load.
I would not trust such a system, since any lapse could blow up the off grid inverter.
Also, you absolutely MUST have a transfer switch to keep the combination of off-grid and GTI inverters from connecting to the grid while they are running in island mode.
Designing such a system safely is not trivial and is not what I would call DIY friendly either.
Anything done without the participation of a knowledgeable licensed electrician would never pass a permit inspection, or if it did would not necessarily be safe anyway.
You would be using the components in a way that was NOT within the manufacturer's design and testing process.
The micro manufacturer may provide instructions on how to configure this kind of use, but that does not by itself make it code approved or even safe.

PS: The problem in general is not the "ripple surge" that you talk about, it is simply excess power production! (With maybe some problems with low power factor loads since the GTI will by default deliver at a unit power factor only. )
Your careless, imprecise, or uneducated use of the relevant terminology make me take everything you say with a large block of salt, and I caution other forum members from jumping into this in the real world without a much better understanding of what is involved.

Your callous nature is what is wrong with information sharing sites like this one. The MagnaSine 4024 does what I listed, a product listed by the manufacturer for the creation of micro-grids. I was just waiting to see which one of you "power users" would jump in to squash another micro-inverter post. I've seen you all over this site. DIY depends upon your level of expertise. Some people like challenges that are simple to solve, such as with a line sensing over-voltage switch to a dump load like a water heater which is very common in solar arrays. I suggest finding someone else to plague with your negative posts because I will not stand for your abuse on mine.

[J.P.M.]

Your callous nature is what is wrong with information sharing sites like this one. The MagnaSine 4024 does what I listed, a product listed by the manufacturer for the creation of micro-grids. I was just waiting to see which one of you "power users" would jump in to squash another micro-inverter post. I've seen you all over this site. DIY depends upon your level of expertise. Some people like challenges that are simple to solve, such as with a line sensing over-voltage switch to a dump load like a water heater which is very common in solar arrays. I suggest finding someone else to plague with your negative posts because I will not stand for your abuse on mine.

Welcome to the forum of straight talk and few illusions.

[SunEagle]

Your callous nature is what is wrong with information sharing sites like this one. The MagnaSine 4024 does what I listed, a product listed by the manufacturer for the creation of micro-grids. I was just waiting to see which one of you "power users" would jump in to squash another micro-inverter post. I've seen you all over this site. DIY depends upon your level of expertise. Some people like challenges that are simple to solve, such as with a line sensing over-voltage switch to a dump load like a water heater which is very common in solar arrays. I suggest finding someone else to plague with your negative posts because I will not stand for your abuse on mine.

solarddy

What inetdog stated was correct and not in any way an action to squash a DIY thread. As a Moderator it is also his responsibility to point out any potential dangers to what others post. He is not abusing you in any way.

Also as a Moderator I will quitely tell you that we will not allow posting that can cause someone to be injured or break any legal rules and will take action to keep people safe. If you do not understand those rules then I would suggest you take you tips somewhere else.

[nomadh]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

[SunEagle]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

I would love to see more manufactures provide grid tie inverters that will continue to produce power from some portion of the pv system when the grid goes down. But except for SMA and some very expensive hybrid inverters there is not much to chose from.

One statement that the OP put out is "I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency on solar arrays employing micro-inverters". The reason for the lack of this type of equipment may have to do with safety or economics. The manufacturers may not feel there is a worthwhile market to produce that type of equipment.

What inetdog and I are trying to say is that some people might be able to "rig up" a system to fool a micro inverter but is it reliable or more important, is it safe? Neither of us feel the "tip" from the OP is safe or reliable.

[lkruper]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

What happens when one needs to sell a house with a complex non-standard system that is only supportable by the expert DIY that built it?

[J.P.M.]

What happens when one needs to sell a house with a complex non-standard system that is only supportable by the expert DIY that built it?

Perhaps it will affect the marketability ? Or the price ? Or limit the potential number of buyers in some way(s) ? While such a system may have some appeal to the DIY and survivalist sets, I'd SWAG it and say they are not a major market segment.

[Naptown]

Enphase has come up with some sort of AC coupled system. This is fairly new as they would void the warranty in the past for these types of installs.
However it is still AC coupled.
A preferable hybrid system IMHO is one that schneider produces.
Array- charge controller-batteries- hybrid inverter.
Issues i have with AC COUPLED i already spelled out
Particularly for back up systems with no generator.

[solardreamer]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

I share your feeling. It's an interesting time for innovation.

Attached is diagram from Magnum that shows how Magasine inverters would work with micro inverters similar to what the OP mentioned. However, it also shows the need for a dump load to soak up excess power to prevent overcharging the batteries as others have mentioned in the thread.

Magnum AC Coupled Line Diagram with Micro Inverters.pdf


I wonder if it's possible to hook up central AC as the dump load.

[solarddy]

I would love to see more manufactures provide grid tie inverters that will continue to produce power from some portion of the pv system when the grid goes down. But except for SMA and some very expensive hybrid inverters there is not much to chose from.

One statement that the OP put out is "I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency on solar arrays employing micro-inverters". The reason for the lack of this type of equipment may have to do with safety or economics. The manufacturers may not feel there is a worthwhile market to produce that type of equipment.

What inetdog and I are trying to say is that some people might be able to "rig up" a system to fool a micro inverter but is it reliable or more important, is it safe? Neither of us feel the "tip" from the OP is safe or reliable.

Not yet understood is another way of saying that. Several products exist, but what I was referring to was a smallish inverter with dump load capability to allow for islanding, I never said to keep the system attached to the grid when doing so, I said to make it automatic so that that could not happen.
As for the rest of that, I'm here to explore new ideas and not discount safety so get off your high horses, you're trotting down the wrong path.

There is a need in the marketplace for a simple inverter that can do what I am talking about. I have a nice MPPT controller that also does wind with a resistor dump. Micro-inverters pose a new challenge to the market and I'm sure even with your skepticism, it will be answered.

Enphase has an article on islanding or using their products offline I suggest you read it. The suggest the 4024 by Magnasine, this tips and tricks post is to show that the specs to do it with are precise, as listed in my OP.

Thanks for the criticism, it keeps our solar world safer.